Seven different towers, including two already under construction, are scrambling to claim the title of Toronto and Canada's tallest building from the current crown-holder at First Canadian Place. The first of what could be several buildings expected to surpass the 300-metre mark, Mizrahi Developments' The One is well under construction at the southwest corner of Yonge and Bloor, as the forming of parking levels and some very unconventional structural engineering unfold just below grade.

Aerial view of The One at Yonge and Bloor, image by Forum contributor Benito

The 308-metre-tall, luxury condominium, hotel, and retail development, designed by Foster + Partners and Core Architects, will feature a hybrid structural exoskeleton that places the tower loads around the exterior, allowing for open column-free floorplans. This complex system involved a special method of foundation construction with deep-bored "mega caissons" that initially added to construction timelines, but is now allowing the attached "super columns" to quickly rise along with the underground parking levels.

Construction at The One, image by Forum contributor Benito

When we last checked in on construction a month ago, the P4 level had been mostly formed and concrete was being poured for the P3 level. The P3 level has since been topped by the P2 level, and after one more level of garage is formed, work will begin on the final underground level, a retail concourse area. Aerial views of the site show the large perimeter supercolumns clearly, which are being installed in sections of rebar cage capped in steel plates before being being poured in with concrete. These columns will continue along the tower's exterior, becoming a primary feature in the building's aesthetic in addition to supporting the tower's structural loads.

Looking south over site of The One, image by Forum contributor thaivic

Forum contributor Contra has been creating a series of diagrams that help illustrate the progress of the building to date, superimposing a cross-section of the site's current state over greyscale elevation diagrams of the building. The latest of these diagrams compares just over one month of progress, during which time almost two full levels were formed despite a minor setback when a small fire broke out on-site in late August.

Progress at The One, diagram by Forum contributor Contra

Additional information and images can be found in our Database file for the project, linked below. Want to get involved in the discussion? Check out the associated Forum thread or leave a comment below.

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